For portable electronic appliances, e.g. electronic watches, pocket calculators, personal digital assistants (PDAs) and cell phones, liquid crystal displays (LCDs) are the most popular displays for revealing the information. Among the displays, a light-reflective LCD is the majority. In order to enhance the displaying ability of the light-reflective LCD in a relatively dark environment, it is preferred that the LCD be imparted thereto light-penetrative feature to some extent Accordingly, a partially light-penetrative and partially light-reflective LCD structure is developed.
Please refer to FIGS. 1A and 1B which are schematic cross-sectional diagrams showing the structure of a conventional partially light-penetrative and partially light-reflective LCD structure with and without applied voltage, respectively. The LCD structure comprises of a back light source 10, a bottom polarizer plate 11, a first wide-band quarter wave plate 12, a transparent bottom glass plate 13, a liquid crystal layer 14, a transparent top electrode 15, a transparent top glass plate 16, a second wide-band quarter wave plate 17, a top polarizer plate 18, and a pixel electrode layer 19. The pixel electrode layer 19 includes a light-penetrative electrode region 191 and a light-reflective electrode region 192 for achieving the functions of partial penetration and partial reflection of the LCD structure.
In a portion of the LCD structure of FIG. 1A including the light-penetrative electrode 191, there is no voltage applied between the pixel electrode 191 and transparent top electrode 15. Therefore, the liquid crystal molecules in the layer 14 are in an initial state and delay light passing therethrough by a phase difference d. Therefore, the overall phase difference of the light provided by the back light source 10 is the sum of a quarter wavelength, the phase difference d and another quarter wavelength, respectively resulting from the delaying effects of the first wide-band quarter wave plate 12, the liquid crystal layer 14 and the second wide-band quarter wave plate 17. That is, the overall phase difference is a half wavelength plus d, and the light delayed by a half wavelength plus d will penetrate the polarizer plate 18 to reach the observer's eyes. This display portion will thus be all-bright. On the other hand, when a voltage is applied between the pixel electrode 191 and transparent top electrode 15, the liquid crystal molecules in the layer 14 will become upright, as shown in FIG. 1B. When all the liquid crystal molecules are upright, the light-phase delaying effect of the liquid crystal layer 14 will be diminished, i.e. d=0. Accordingly, the overall phase difference becomes a half wavelength. The light with such phase difference is not allowed to penetrate the polarizer plate 18, and thus this display portion will be all-dark.
Further, in another portion of the LCD structure of FIG. 1A including the light-reflective electrode 192, there is no voltage applied between the pixel electrode 191 and the transparent top electrode 15. Therefore, the liquid crystal molecules in the layer 14 is in an initial state and delay light passing therethrough two times by a phase difference 2d. Therefore, the overall phase difference of the light provided by the back light source 10 is the sum of a quarter wavelength, the phase difference 2d and another quarter wavelength, respectively resulting from the delaying effects of the second wide-band quarter wave plate 17, twice the liquid crystal layer 14 and the second wide-band quarter wave plate 17 again. That is, the overall phase difference is a half wavelength plus 2d, and the light delayed by a half wavelength plus 2d will penetrate the polarizer plate 18 to reach the observer's eyes. This display portion will thus be all-bright. On the other hand, when a voltage is applied between the pixel electrode 192 and transparent top electrode 15, the liquid crystal molecules in the layer 14 will become upright, as shown in FIG. 1B. When all the liquid crystal molecules are upright, the light-phase delaying effect of the liquid crystal layer 14 will be diminished, i.e. d=0. Accordingly, the overall phase difference becomes a half wavelength. The light with such phase difference is not allowed to penetrate the polarizer plate 18, and thus this display portion will be all-dark.
The first wide-band quarter wave plate 12 or the second wide-band quarter wave plate 17 is conventionally provided by overlapping a quarter wave plate and a half wave plate. In order to achieve the wide-band function and make the light within a certain wavelength range have a phase difference of a quarter wavelength, the relationship among the slow axes S1 and S2 of the quarter and the half wave plates and the transmission axis T of the bottom polarizer plate 11 or the top polarizer plate 18 is required to be in a certain manner, for example as shown in FIG. 2. Therefore, the manufacturing and assembling of the wide-band quarter wave plate 12 or 17 is complicated, and the cost is high.